Molecular beam epitaxy of GaN(0001) utilizing NH3 and/or NH+x ions: Growth kinetics and defect structure

Gas-source molecular beam epitaxy (GS-MBE), utilizing Ga and NH3, and reactive-ion MBE (RIMBE), incorporating both thermal NH3 and low-energy NH+x ions, were used to grow single crystal GaN(0001) layers on Al2O3(0001) at temperatures Ts between 700 and 850 degree C with deposition rates of 0.2--0.5 μm h-1. The RIMBE experiments were carried out with incident NH+x/Ga flux ratios JNH+x/JGa=1.9--3.2 and NH+x acceleration energies ENH+x=45--90 eV. Plan-view and cross-sectional transmission electron microscopy analyses showed that the primary defects in the GS-MBE films were threading dislocations having either pure edge or mixed edge/screw characteristics with Burgers vectors bar b=1/3 left-angle 2 bar 1 bar 10 right-angle, basal-plane stacking faults with displacement vectors bar R=1/6 left-angle 02 bar 23 right-angle, and prismatic stacking faults with bar R=1/2 left-angle bar 1101 right-angle. In the case of RIMBE films, no stacking faults or residual ion-induced defects were observed with ENH+x=45 eV and Ts≥800 degree C. However, increasing ENH+x to ≥60 eV at Ts=800 degree C gave rise to the formation of residual ion-induced point-defect clusters observable by transmission electron microscopy (TEM). Increasing Ts to 850 degree C with ENH+x≥60 eV resulted in the ion-induced defects aggregating to form interstitial basal and prismatic dislocation loops, whose number densities depended upon the ion flux, with Burgers vectors 1/2 left-angle 0001 right-angle and 1/3 left-angle 2 bar 1 bar 10 right-angle, respectively. (Abstract Truncated)